FIG. 5 illustrates an example of a CT scanner 100 as one type of medical equipment. The CT scanner 100 diagnoses and analyzes a pathological symptom through irradiation with an X-ray or the like. The CT scanner 100 includes an examination unit 101 having an opening 101A, and a bed unit 102 movable in the opening 101A of the examination unit 101 with an examinee 110 such as a human body lying thereon. The examination unit 101 includes a ring-shaped rotator 105 (gantry) having an X-ray irradiation device 103 and a detection unit 104 arranged so as to be opposed to each other in a diameter direction. The rotator 105 is rotatably supported by a cylindrical stationary unit 106 through intermediation of a bearing 51.
The CT scanner 100 rotates the rotator 105 about the bed unit 102 while irradiating the examinee 110 with an X-ray from the X-ray irradiation device 103 so as to detect the X-ray having passed through the examinee 110 with the detection unit 104, thereby obtaining a tomographic image of the examinee 110.
In the CT scanner 100, in order to form the opening 101A of the examination unit 101 into such a dimension that the examinee 110 may pass through the opening 101A (diameter of about 1 m), and to downsize the CT scanner 100 itself, it is necessary to reduce a space of a rotation support unit 107 having the bearing 51 arranged therein. Therefore, a so-called ultrathin double-row rolling bearing having a significantly small ball diameter with respect to a pitch circle diameter of balls is used as the bearing 51. In this case, the ultrathin rolling bearing refers to an ultrathin large-scale rolling bearing having an inner diameter of 650 mm or more and having a value of a ratio Db/PCD of a diameter Db of each of rolling elements to a pitch circle diameter PCD of the rolling elements of 0.03 or less.
Patent Document 1 discloses such an ultrathin double-row rolling bearing that an inner member is formed of a pair of raceway rings, which are fastened with a fitting structure while a concentric state is kept. FIG. 9 illustrates this double-row rolling bearing. The double-row rolling bearing 51 mainly includes an outer member 52, an inner member 53, rolling elements 54, and retainers 55. The double-row rolling bearing is a double-row angular ball contact bearing having balls 54 arranged in two rows as the rolling elements. The balls 54 and 54 assembled into a space between each of two rows of raceway surfaces 56 and 56 of the outer member 52 and each of two rows of raceway surfaces 57 and 57 of the inner member 53 are brought into contact with the raceway surfaces 56 and 57 at a contact angle, and the double-row angular ball contact bearing is constructed in back-to-back arrangement so as to be suitable for supporting a moment load.
The inner member 53 is formed of a pair of raceway rings 53a and 53b. The raceway ring 53a has a screw hole 58a, and the raceway ring 53b has a fit-insertion hole 58b. The raceway rings 53a and 53b are fastened with a bolt 59. In this case, due to the fitting structure formed by a projection 60a formed on the raceway ring 53a and a recess 60b formed on the raceway ring 53b, misalignment between the raceway rings 53a and 53b is prevented. The bolt 59 is fastened to pressurize the raceway ring 53b toward the raceway ring 53a side, thereby applying a preload (minus clearance) to the inside of the bearing.